1. Field of the Invention
The present invention relates to illumination-type rotary variable resistors used for controlling the temperature and wind direction of car air conditioners and the sound volume and quality of video and audio equipment.
2. Background Art
Rotary variable resistors with an annular cross section are commonly used as equipment controls. The increasing sophistication of equipment and the trend for centralization of operating units have led to building switches and other electronic components into rotary variable resistors and mounting them on equipment wiring boards.
Concerning rotary variable resistors, illumination-type rotary variable resistors which have a light-emitting diode (LED) built into the operating unit are increasingly used. The LED is built in to indicate the position to which the resistor has been rotated when in use.
An LED built-in rotary variable resistor is described next as a conventional illumination-type rotary variable resistor, with reference to FIGS. 9 to 12.
FIG. 9 is a side sectional view, FIG. 10 is an exploded perspective view, FIG. 11 is a sectional view of a key part showing a section taken along Line 11—11 in FIG. 10 in its center portion, and FIG. 12 is a plan view illustrating the relation of an insulating substrate and slider which are key parts of the conventional rotary variable resistor with built-in LED.
In FIGS. 9 to 12, housing 1 has an approximately round center hole 1A at its center. Housing 1 is an insulating resin housing with an annular cross section.
A wall surrounding center hole 1A protrudes upward to form cylinder 1B.
An annular portion of housing 1 is cavity with an open top. In other words, cylinder 1B, round bottom plate 1C, and outer wall 1D create cavity 1E.
Annular insulating substrate 2 is housed and held in cavity 1E.
LED conductive film 3 including anode conductive film 3A and cathode conductive film 3B are printed to be formed on a top face of insulating substrate 2 at the inner radius.
Resistor film 4 including resistance film 4A and conductive film 4B are concentrically printed to be formed on insulating substrate 2 at the outer radius of LED conductive film 3.
Terminal 5 for coupling to an outer electrical circuit (not illustrated) of the illumination-type rotary variable resistor is connected to the end of each film.
Insulated resin operating knob 6 has flange 6B on its outer radius beneath cylindrical operating member 6A. An inner face of operating member 6A is fitted in rotatable fashion to an outer face of cylinder 1B of housing 1.
When operating member 6A and cylinder 1B are fitted together, flange 6B is housed in cavity 1E of housing 1. Resistor slider 7 which resiliently contacts and slides on resistor film 4, and anode slider 8 and cathode slider 9 which resiliently contacts and slides on LED conductive film 3 are provided on the bottom face of flange 6B.
The top face of operating knob 6 assembled in rotatable fashion on housing 1 as described is supported by cover 10. This cover 10 is attached in a way such as to cover cavity 1E of housing 1 containing flange 6B.
Cylindrical operating member 6A and cylinder 1B of housing 1 protrude upward from center hole 10A in cover 10.
As shown in FIG. 10, spring member 14 is attached to cover 10. Spring member 14 has retainer 14B at its center. This retainer 14B engages tooth 6G created on flange 6B of operating knob 6. Retainer 14B is pressed against tooth 6G by springs 14A on both its sides. This allows operating knob 6 to be held reliably at the rotated position to maintain the set resistance.
As shown in FIGS. 10 and 11, LED through hole 6C is created such as to pass vertically through in a radial thickness of cylindrical operating member 6A of operating knob 6.
A portion of anode slider 8 perpendicularly bent upward is further processed to create dogleg LED contact 8B. In the same way, a portion of cathode slider 9 perpendicularly bent upward is further processed to create dogleg contact 9B.
LED contact 8B and LED contact 9B are inserted into LED through hole 6C in such a way that these contacts 8B and 9B face each other inside LED through hole 6C. Projection 6D provided on a bottom face of flange 6B is flattened and deformed such as to secure anode slider 8 and cathode slider 9. In this way, anode slider 8 and cathode slider 9 are fixed to the bottom face of flange 6B.
LED 11 is inserted from the top into LED through hole 6C in operating member 6A. Bottom ends of two LED terminals 11A, the anode and cathode of LED 11, are cut at a bevel to a predetermined length from the end so as to form a sharp point at each tip. These two LED terminals 11A bend the top of dogleg LED contacts 8B and 9B, and resiliently contact anode slider 8 and cathode slider 9.
LED conductive film 3 and resistor film 4 are disposed on annular insulating substrate 2.
FIG. 12 shows further details of substrate 2. Cathode conductive film 3B and anode conductive film 3A are disposed as LED conductive film 3, and conductive film 4B and resistance film 4A are printed to be formed as resistor film 4 in these sequences from the inner radius.
Each film is annular, with the same center, and disposed electrically insulated from each other.
Anode slider 8 has conductive film contact 8A whose tip is split into two contacts and which slides on anode conductive film 3A. Contact 8A extends away from the insertion position of LED 11 in the direction opposite to the circumferential direction of LED contact 8B.
Cathode slider 9 has conductive film contact 9A whose tip is split into two contacts and which slides on cathode conductive film 3B. Contact 9A extends away from the insertion position of LED 11 to the direction opposite to the circumferential direction of LED contact 9B.
Resistor slider 7 has conductive film contact 7A whose tip is split into two contacts and resistance film contact 7B whose tip is split into three contacts. Each contact resiliently contacts and slides on conductive film 4B and resistance film 4A.
Conductive film contact 7A and resistance film contact 7B resiliently contact conductive film 4B and resistance film 4A respectively at radially aligned positions.
In the above configuration, resistor slider 7 slides on resistance film 4A and conductive film 4B when operating knob 6 is rotated so that a predetermined resistance is gained from electrically coupled terminal 5.
LED 11 emits light when powered by the current passing between anode conductive film 3A and cathode conductive film 3B through anode slider 8 and cathode slider 9 so as to clearly indicate the operating position of operating knob 6.
One known prior technical document related to the conventional illumination-type rotary variable resistor described above is the Japanese Laid-open Application No. 2001-305259.
This conventional illumination-type rotary variable resistor provides a dogleg bend on LED contacts 8B and 9B of LED sliders 8 and 9. In addition, LED sliders 8 and 9 are bent approximately perpendicularly to the attachment face that is the bottom face of flange 6B.
Furthermore, LED contacts 8B and 9B are inserted and fixed to LED 11 through hole 6C in operating knob 6 in a way not to deform contacts 8B and 9B when attaching LED sliders 8 and 9.
With respect to workability, the above processing and attachment are not always efficient.
In addition, it is often preferable to cut the tip of LED terminal 11A at a bevel before inserting LED 11. This is because a beveled tip makes it easy to bend dogleg LED contacts 8B and 9B of LED sliders 8 and 9 using two LED terminals 11A when LED 11 is inserted into LED through hole 6C in operating knob 6.